The present invention relates to a manufacturing method for a plasma display panel used as a display for a color television set or the like.
In recent years, Plasma Display Panel (hereafter referred to as PDPs) have attracted attention as large-scale, thin, lightweight displays for use in computers and televisions. This has resulted in an increasing demand for high-definition PDPs.
FIG. 16 is a simplified sectional view showing an example of a typical alternating current (AC) type PDP.
In the figure, display electrodes 102 are formed on a front glass substrate 101. These are then covered by a dielectric glass layer 103 and a protective layer 104 made of magnesium oxide (MgO) (see, for example, Japanese Laid-Open Patent No. 5-342991).
Address electrodes 106 and barrier ribs 107 are formed on a back glass substrate 105. Phosphor layers 110 to 112 of respective colors (red, green, and blue) are formed in spaces between the barrier ribs 107.
The front glass substrate 101 is then placed on the barrier ribs 107 on the back glass substrate 105. A discharge gas is supplied into the spaces between the substrates 101 and 105 to form discharge spaces 109.
In the above PDP, vacuum ultraviolet rays (their wavelength is mainly at 147 nm) are emitted as electric discharges occur in the discharge spaces 109. The phosphor layers 110 to 112 of respective colors are excited by the emitted vacuum ultraviolet rays, resulting in color display.
The following is an explanation of a manufacturing method for the above PDP.
The display electrodes 102 are formed by applying a silver paste to the surface of the front glass substrate 101, and baking the applied silver paste. The dielectric layer 103 is formed by applying a dielectric glass paste to the surface of the layers, and baking the applied dielectric glass paste. The protective layer 104 is then formed on the dielectric glass layer 103.
The address electrodes 106 are formed by applying a silver paste to the surface of the back glass substrate 105, and baking the applied silver paste. The barrier ribs 107 are formed by applying a glass paste to the surface of the layers with a certain pitch, and baking the applied glass paste. The phosphor layers 110 to 112 are formed by applying pastes of phosphors of respective colors to the spaces between the barrier ribs 107, and baking the applied pastes at around 500xc2x0 C. to remove resin and other elements from the pastes.
After the phosphors are baked, a sealing glass frit is applied to a peripheral region of the front glass substrate 101 or of the back glass substrate 105, and the applied sealing glass frit is baked at around 350xc2x0 C. to remove resin and other elements from the applied sealing glass frit thereby forming a glass sealant layer. (Frit Pre-baking Process)
The front glass substrate 101 and the back glass substrate 105 are put together in such a manner that the display electrodes 102 and the address electrodes 106 face each other at right angles. The substrates are then sealed by heating them to a temperature (around 450xc2x0 C.) higher than a softening point of the glass sealant layer. (Sealing Process).
The panel composed of the sealed substrates is then heated to a temperature of around 350xc2x0 C. while air is being removed from an inner space formed between the substrates (the space is formed between the front glass substrate and the back glass substrate, and the phosphor layers are exposed to the space). (Exhausting Process). After the exhausting process is complete, the discharge gas is supplied to the inner space at a certain pressure (typically, in a range of 4xc3x97104 Pa to 7xc3x97104 Pa).
One issue is how to improve the luminance and the color reproduction of the PDP manufactured as above.
In view of the above issue, the phosphors used to form the phosphor layers have been improved. However, it is also desirable to consider improving the luminance and the color reproduction by improving the manufacturing process of the PDP.
The object of the present invention is to provide a PDP which exhibits high light-emitting efficiency and superior color reproduction. The above object can be achieved by the following. In the process where a sealant layer is formed on at least one of peripheral regions of the facing sides of the front panel and the back panel, a shape of the sealant layer is set so that at least one gap is provided between the panels. The gaps serve as passages between the inner space of the PDP and the outside of the PDP.
As a specific way to provide at least one gap between the peripheral regions of the panels when the panels are placed facing each other, the sealant layer is formed so as to have at least one protrusion or one depression. Alternatively, a sealant layer is formed around one of the peripheral regions of the substrates, and another sealant layer is formed at least on one part of the other one of the peripheral regions of the substrates.
The following is an explanation of the effects produced by the present invention.
During a manufacturing process of a PDP, blue phosphors are deteriorated by heat as the phosphor layers which have been formed are heated in the sealing process. This lowers the intensity and the chromaticity of the emitted light. The inventors of the present invention have found that this heat deterioration in the blue phosphors is more likely to occur when the phosphor layers are heated in an atmosphere that contains a large amount of moisture, and is less likely to occur when the phosphor layers are heated in an atmosphere that contains little moisture.
Here, with a conventional method for manufacturing a typical PDP, moisture absorbed by the substrates (especially by the MgO protective layer) evaporates into the inner space when a sealant layer placed between the front substrate and the back substrate is heated. As the moisture is trapped within the inner space, the phosphors are exposed to an atmosphere containing a large amount of moisture at a high temperature. In such a situation, the phosphors are easily deteriorated by heat.
In contrast, according to the PDP manufacturing method of the present invention, gaps through which a gas can circulate are maintained at the periphery of the PDP until the sealant layer is heated to a temperature of a softening point of the sealant layer. Therefore, the moisture that has been evaporated into the inner space can escape, instead of being trapped within the inner space. This prevents the phosphors from being exposed to an atmosphere containing a large amount of moisture.
As described above, the heat deterioration in the phosphors (especially in the blue phosphors) during the sealing process can be prevented in accordance with the PDP manufacturing method of the present invention.
Here, if the sealing process in which a sealant layer is heated is carried out in a dry gas atmosphere or in a decreased pressure atmosphere, the heat deterioration in the phosphors can be more effectively prevented.
Here, xe2x80x98dry gasxe2x80x99 refers to a gas containing steam with a lower partial pressure than the typical partial pressure. It is especially preferable to use air that has been subjected to a drying process (dry air).
It is desirable that the partial pressure of the steam in the dry gas atmosphere is set at 10 Torr (1300 Pa) or lower, and more preferably at 5 Torr (650 Pa) or lower, or at 1 Torr (130 Pa) or lower. It is desirable that the dew-point temperature of the dry gas is set at 12xc2x0 C. or lower, and more preferably at 0xc2x0 C. or lower, or at xe2x88x9220xc2x0 C. or lower.
It is preferable to carry out not only the sealing process but also the baking process of the phosphors, the pre-baking process of the sealant, and the exhausting process in the dry gas atmosphere, so that the heat deterioration in the phosphors during these processes can also be prevented. This greatly improves light-emitting characteristics of the blue phosphors used in the PDP.
By manufacturing a PDP in accordance with the method of the present invention, the chromaticity coordinate y (CIE color specification) of light emitted from blue cells of the PDP when only the blue cells emit light, or of light emitted when the blue phosphors are excited by vacuum ultraviolet rays can be made 0.08 or lower. Moreover, the peak wavelength of a spectrum of light emitted from blue cells of the PDP when only the blue cells emit light can be made 455 nm or lower.
By improving the chromaticity of emitted light of the blue phosphors, color reproduction of the PDP is also improved. The color temperature in the white balance, that is, the color temperature of the emitted light when all cells emit light on the same power condition can be made 9000K or higher.